A plurality of light-emitting diodes (LEDs) may be assembled together in high-efficiency and high-brightness lighting applications. The brightness of LEDs directly may be directly related to the current flowing through the LEDs. In general, the LEDs may be much brighter as the current is higher. In order to achieve balanced-brightness between a plurality of LEDs, multiple LEDs may be connected in series, and a primary controlled flyback may be utilized as a driver for the LEDs. As shown in FIG. 1, a current flowing through the LED strings can be controlled by controlling switch Q1 according to a primary current. However, only one LED string can be driven by this topology, and if the quantity of series connected LEDs is more than a certain number, the voltage across the LED string may be much higher. As a result, the withstand voltage of the rectifier diode may be increased to meet the requirements, and it may be difficult to improve system conversion efficiency. In addition, design and production costs may be increased as a large bulk capacitor is employed as the filter capacitor.